Author Topic: 74 TX500- completely dumbfounded  (Read 97 times)

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Offline CallaghanWilliams

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74 TX500- completely dumbfounded
« on: September 11, 2019, 01:26:48 AM »
So, I bought this bike (first bike I've ever actually owned) in April. The young man I bought it from was real up front about what it was and what he'd done to it. He said the coils used to overheat on him and so he'd replaced them with 3ohm aftermarket coils as well as a contactless electronic ignition unit, he also replaced the carbs with a set from a 76 xs500 since the original carbs had that dual cable system. The signal lights had been upgraded to LED's and the relay to match. The bike ran well, albeit with that bucket of bolts sounding starter chain. It ran for several months, rode it all over. Ran the carbs dry and parked it in my garage for 6 weeks with non-ethanol fuel and some fuel stabilizer when I left for a summer work trip. No big deal.

Came back, started right up. Rode it for two or three days.
The last day it suddenly died after having the throttle open and letting off to come to a stop.
It progressively started dying at idle over the next few hours. I increased the idle screw just to get me home.
It died once again a couple miles from my house, and refused to start again (Kick or electric)
Had to have it towed home.

I've been through everything I can think of,
Drained the tank (no water)
Fresh non-ethanol Fuel.
New fuel lines.
Cleaned the carbs twice.
Has spark and two new spark plugs.
Battery is charged and holding a consistent 12+ volt charge.
Battery doesn't dip below 11V when starting.
Even tried starting spray....

Anybody got anything for Me?

Thanks
-John

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Re: 74 TX500- completely dumbfounded
« Reply #1 on: September 11, 2019, 04:20:41 AM »
Are the plugs coming out wet? If wet and you have spark are you getting any pops or kick backs on the starter lever? If so, suspect your electronic ignition timing. If spark but dry plugs then it's fuel related and you should double check fuel flow to the carbs.

Guy
Now Retired Yamaha guy. Cut me and I bleed "Cinquasia Red"

Offline Garn

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Re: 74 TX500- completely dumbfounded
« Reply #2 on: September 11, 2019, 05:27:16 AM »
I'm thinking that original trouble, overheating of the coils, hence, being replaced. This fault may have been the regulator/ rectifier.... Check with bike running should range up to but not exceeding 14.0 volts too much, with bike running at 3000 Rpm. I would look there first!
Check petrol cocks are giving good flow, they do give trouble clogging up.
Here is an onside chance.... Some bikes have restrictors in exhaust and inlet from new. They are purely a large washer with a smaller than usual hole in them to restrict the speed and acceleration of these small bikes with young riders.
Another item could be missing small rubber o-rings or plugs missing from main jets (don't know the effect of missing these).
RegardZ.

PS.. What type of electronic ignition?. Could be mismatch with electronic ignition and 3 ohm coils.
PPS.. Also check starting current of battery, although it seems to check out. Check if blinkers are slow and generally all electrical is working.vo
« Last Edit: September 11, 2019, 05:37:56 AM by Garn »
Kawasaki Z1, Z1A, Z1B, Z900-A4 and TX500A
    Sydney, Australia

Offline CallaghanWilliams

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Re: 74 TX500- completely dumbfounded
« Reply #3 on: September 11, 2019, 10:35:14 PM »
Is there a way to check the rectifier if I can't get the bike to run?

Offline CallaghanWilliams

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Re: 74 TX500- completely dumbfounded
« Reply #4 on: September 11, 2019, 10:36:43 PM »
Also the electronic ignition unit is a newtronics brand purchased from YamBits.com

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Re: 74 TX500- completely dumbfounded
« Reply #5 on: September 12, 2019, 03:28:50 AM »
There are checks for rectifier function but it has nothing to do with the ignition or starting. If your battery is staying charged then look somewhere else for the non-start problem.

Guy
Now Retired Yamaha guy. Cut me and I bleed "Cinquasia Red"